How good can you develop, let's say something easy, for example some python + Postgres + node.js on a Chromebook like the Pixel Slate without rooting or removing ChromeOS?
Provided the Linux container system works well on it - it should be easily possible. Whether the UX is good for a developer workflow I can't be sure. Users at reddit.com/r/chromeos seem to be able to do some good dev work on crostini-enabled devices.
You can’t run docker normally on ChromeOS you can run it on some chromebooks that support dual booting with something like GalliumOS, or rooting the machine and running your Linux distro in a container/chroot.
Unless you are severely strapped for cash and can’t find the same low end chromebook hardware in a low end windows form factor that can be simply reinstalled over there is absolutely no reason to even consider using a chromebook for anything other than it was intended unless you are rooting it for a hobby.
People abuse the fact that you can sometimes find them for sub $200 for $300-400 worth of hardware but it’s a hack on top of a hack to make it run anything.
The whole point of a Chromebook is simplicity. Except for maybe saving a couple hundred bucks (as you say)--which I'm guessing isn't really much of a good reason for most of the people doing this--it doesn't make a lot of sense. There's plenty of cheap generation or two back laptop hardware that you can reliably install Linux on and call it a day.
If I want to do software development etc. I'll use my Linux laptop. If I just need something simple for travel, I'll take a Chromebook.
Any Crostini supported device works fine. Obviously more RAM and better CPU means a better experience.
I have a basic Acer with a Celeron and 4GB of RAM. Been running VS Code and node to develop React Native apps. Can even load the Expo Android app from the Play Store, no separate Android device required!
Not sure about the slate, but I have a Pixelbook, which is my personal laptop, and the crostini Linux integration is great for development. Specifically, I use it for Rust programming, and have compiled a couple of C++ projects too.
The Terminal app that comes with the Linux install is good, supports tmux etc.
There is clipboard integration between the pixelbook host and the container. File sharing is also easy with the file manager being able to drag andd drop files in and out of the container.
I can use Firefox inside the container, which is what I usually use to browse.
Theoretically you have access to the lxc tool inside the top level container, so you could create multiple containers and possibly set up complicated networking setups between them, but I've not tried this.
I've done Python webapp development on an unmodified Chromebook that supported Android apps via Termux. The only catch was that the network layer doesn't make 127.0.0.1 the same for Chrome and Android so I ended up testing in Android Firefox, which is hilarious but worked fine.